Plasma monitoring method and plasma monitoring system

ABSTRACT

A plasma monitoring method using a sensor, the sensor having a substrate; a first electrode, the first electrode being a conductive electrode and formed on the substrate while being isolated from the substrate; an insulating film formed on the first electrode; a contact hole formed in the insulating film and having a depth from a surface of the insulating film to the first electrode; and a second electrode, the second electrode being a conductive electrode, formed on the surface of the insulating film, and faced to plasma during a plasma process, the plasma monitoring method including measuring and monitoring potentials of the first electrode and the second electrode or a potential difference between the first electrode and the second electrode during the plasma process is disclosed. A plasma monitoring system carrying out the plasma monitoring method is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 from Japanese PatentApplication No. 2007-225677, the disclosure of which is incorporated byreference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plasma monitoring method applicableto a semiconductor manufacturing processes (steps) and all the othermanufacturing processes using plasma and a plasma monitoring systemtherefor.

2. Description of the Related Art

There is a conventional technique related to a plasma monitoring methodand a plasma monitoring system for monitoring a processing on a waferdisposed in a plasma processing apparatus as disclosed in, for example,Japanese Patent Application Laid-Open (JP-A) Nos. 2003-282546 and2005-236199.

FIG. 7 is a schematic configuration diagram showing a conventionalplasma monitoring system disclosed in the JP-A Nos. 2003-282546 and2005-236199.

The plasma monitoring system includes a plasma processing apparatus 10.The plasma processing apparatus 10 is an apparatus applying a radiofrequency (hereinafter, “RF”) bias to a plasma chamber 11 set in avacuum to generate plasma 12 within the plasma chamber 11, andperforming such processings as etching and film formation on a wafer 20that is a monitoring target workpiece disposed on a stage 13. Avoltmeter 15 for self-alignment bias measurement is connected to thestage 13 via a coil 14 for alternating current (hereinafter, “AC”)voltage component elimination. A sensor 21 or the like for plasmaprocess detection is bonded onto the wafer 20.

If a plasma process is to be monitored, then the plasma 12 is generatedin the plasma chamber 11 by application of the RF bias to the plasmachamber 11, and the plasma process (e.g., plasma etching) is performedon the wafer 20. At this time, by monitoring a voltage detected by thesensor 21, a plasma etching end point may be detected and the wafer 20may be worked with high accuracy.

It is generally known that energy of ions generated from the plasma 12during the plasma etching influences a shape and a size of a pattern ofthe wafer 20 and electrically damages the wafer 20. Due to this, it isimportant to observe energy of ions incident on the wafer 20 from theplasma 12 and an ion energy distribution. However, since the ionincident energy if ions may not be directly measured, a self-alignmentbias is monitored and set as an indirect index. Normally, the voltmeter15 disposed below the stage 13 within the plasma chamber 11 measures anaverage value of the self-alignment bias. Since the self-alignment biasis an AC voltage, the coil 14 eliminates RF component in the AC voltageso that the voltmeter 15 may measure only a constant direct-current(hereinafter, “DC”) voltage.

FIG. 8 is a schematic diagram explaining the self-alignment bias. Asshown in a state 1, when the wafer 20 is exposed to the plasma 12, theplasma 12 is in a state in which electrons e and positive ions h areslightly separated. Both the electrons e and the positive ions h move tobe charged onto the wafer 20. However, at this time, the electrons emore faster and a large quantity of electrons e are charged onto thewafer 20 (and onto the stage 13 if the stage 13 is present under thewafer 20) since the electrons e are far lighter than the positive ionsh. Due to this, as shown in a state 2, a potential of the wafer 20 turnsnegative by the charging of the electrons e on the wafer 20.

As shown in a state 3, the positive ions h which are oppositely chargedto electrons e, and which move faster than electrons, arrive at thewafer 20. However, the amount of the positive ions h is not so large asto cancel the electrons e previously charged at the wafer 20. Due tothis, ultimately both the negative electrons e and the positive ions hfrom the plasma 12 arrive at the wafer 20 and are charged thereat.However, since a charge amount of the initial negative electrons e (inthe state 1) is larger, the potential of the wafer 20 is negative in astable state. This negative potential is referred to as self-alignmentbias.

Nevertheless, the conventional plasma monitoring methods and plasmamonitoring systems have a first problem (1) and a second problem (2) asfollows.

(1) First Problem

In a working process of forming a large scale integrated circuit(hereinafter, “LSI”) on the wafer 20, plural contact holes is formed,for example, by plasma etching. However, both a potential of a surfaceof the wafer 20 and that of a bottom of each contact hole may not bemonitored in the conventional technique. Due to this, charge offsetcaused by trapping of charges (charge-up) may not be measured. If anaspect ratio (a ratio of a depth of each contact hole to a diameterthereof) is high, it is difficult for the electrons e to arrive atbottoms of the contact holes (electron blocking effect). As a result,the electrons e are insufficiently supplied to the bottoms of thecontact holes, thereby making the bottoms of the contact holespositively charged up as compared with a surface of a contact holepattern. These respects provoke such problems as dielectric breakdown oftransistors, reduction in etch rate, and insufficient progress ofetching. The charge-up problem is serious since the diameter of eachcontact hole in and after the advanced 65-nanometer (nm) generation is0.1 micrometer (μm) and the aspect ratio of the contact hole is as highas about 10.

Generally, a recording memory transistor (Non-Volatile MemoryTransistors (hereinafter “NVM”)) or a wafer (blank wafer), on which nocircuit pattern is formed, is employed to monitor a charge-up amount.However, even with use of the NVM or the blank wafer, neither themeasurement of a charge-up amount on an actual pattern nor that of acharge-up amount at real time may not be advantageously made. A problemrelated to the NVM (hereinafter, “(a) NVM-related Problem”) and aproblem related to the blank wafer (hereinafter, “(b) blankwafer-related Problem”) will be described in detail.

(a) NVM-Related Problem

In case of the NVM, an antenna (a conductor) on the surface of a wafer20 exposed to the plasma 12 is connected to a gate electrode of the NVMburied in the wafer 20. A transistor characteristics (easiness ofcurrent flow between a source electrode and a drain electrode) of theNVM changes according to a magnitude of a potential applied to the gateelectrode of the NVM. Due to this, if charge-up occurs on the NVMcharge-up monitoring wafer 20, charges are trapped into the antenna anda potential of the antenna changes. Since the antenna is connected tothe gate electrode of the NVM, the characteristic of the NVM changesaccording to a potential of the antenna. Namely, an amount of a changein the transistor characteristics may be recognized from a magnitude ofa charge-up amount (a potential change width). Therefore, if thecharge-up occurs on the NVM charge-up monitoring wafer 20, then chargesare trapped into the antenna and the antenna potential changes. Sincethe antenna is connected to the gate electrode of each NVM, the NVMcharacteristic changes according to the magnitude of the antennapotential. Namely, the magnitude of the charge-up amount (potentialchange width) may be confirmed from the change amount of the transistorcharacteristics. Accordingly, in case of the NVM, the sensor wafer 20that is the monitoring target workpiece is temporarily exposed to theplasma 12 to change the NVM characteristic, the sensor wafer is takenout from the plasma 12, and how much the NVM characteristic changes (achange amount of the easiness for current flow across the NVM) beforeand after the exposure to the plasma 12 is measured using a measuringinstrument.

Therefore, if the charge-up occurs in the atmosphere of the plasma 12,the charge-up (e.g., antenna potential) may not be observed at realtime. Further, since the antenna (conductor) is flat and the flatantenna (conductor) receives (picks up) the charge-up, the charge-upthat occurs in a pattern of an actual LSI product such as contact holemay not be measured.

(b) Blank Wafer-Related Problem

The blank wafer means a wafer configured so that only a silicon oxidefilm or a silicon nitride film is formed simply on one surface of asilicon substrate. If the wafer 20 having such an insulating film formedon the silicon substrate is exposed to the plasma 12, a surface of theinsulating film is charged up. Next, when the wafer 20 is taken out fromthe plasma chamber 11, charges trapped onto the insulating film remain(as a charge-up residue). This charge-up residue is measured using anoncontact potential measuring instrument to thereby measure a charge-updegree. As can be seen, if the blank wafer is used, the measurement ismade after the sensor wafer 20 is taken out from the atmosphere of theplasma 12 and not made when charge-up actually occurs in the atmosphereof the plasma 12. Therefore, the charge-up may not be measured at realtime. Besides, since the insulating film is a plain film without apattern on the silicon substrate, the charge-up may not be measured inan actual pattern including contact holes.

(2) Second Problem

Since the energy of ions incident on the wafer 20 from the plasma 12 maynot be directly measured, the self-alignment bias is monitored and usedas an indirect index. Normally, the average value of the self-alignmentbias is measured by the voltmeter 15 disposed below the stage 13. Due tothis, an in-plane distribution of the self-alignment bias may not bemeasured. This second problem will be described in detail.

As shown in FIG. 7, normally, the stage 13 is a conductive electrode. Ifthe self-alignment bias is generated in the atmosphere of the plasma 2,the self-alignment bias is applied to portions (such as an outercircumference) of the stage 13 to which portions the plasma 12 isexposed. The voltmeter 15 is disposed below and connected to the stage13, and measures the self-alignment bias. Due to this, theself-alignment bias is measured while using an entire area of theportions (e.g., the outer circumference) of the stage 13 to whichportions the plasma is exposed as an antenna. As a result, how theself-alignment bias differs among plural points on the wafer 20 (on thestage 13) and the like may not be measured. In FIG. 7, the average valueof the self-alignment bias with the outer circumference of the stage 13set as an antenna (i.e., the average value of each self-alignment biasesthat possibly slightly differ among various points on the outercircumference of the stage 13) is measured.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda plasma monitoring method using a sensor, the sensor comprising:

a substrate;

a first electrode, the first electrode being a conductive electrode andformed on the substrate and electrically isolated from the substrate;

an insulating film formed on the first electrode;

a contact hole formed in the insulating film and having a depth from asurface of the insulating film to the first electrode; and

a second electrode, the second electrode being a conductive electrode,formed on the surface of the insulating film, and facing a plasma duringa plasma process, the plasma monitoring method comprising:

measuring and monitoring potentials of the first electrode and thesecond electrode or a potential difference between the first electrodeand the second electrode during the plasma process.

According to a second aspect of the invention, there is provided aplasma monitoring system comprising:

a sensor having a substrate; a first electrode, the first electrodebeing a conductive electrode and formed on the substrate andelectrically isolated from the substrate; an insulating film formed onthe first electrode; a contact hole formed in the insulating film andhaving a depth from a surface of the insulating film to the firstelectrode; and a second electrode, the second electrode being aconductive electrode, formed on the surface of the insulating film, andfacing a plasma during a plasma process; and

a voltmeter measuring potentials of the first electrode and the secondelectrode or a potential difference between the first electrode and thesecond electrode during the plasma process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a plasma process detectionsensor included in a plasma monitoring system according to Example 1 ofthe present invention;

FIG. 2 is a schematic configuration diagram of the plasma monitoringsystem according to Example 1 of the invention;

FIGS. 3A to 3I are schematic cross-sectional step views showing each oneof the steps of an exemplary method of manufacturing the plasma processdetection sensor shown in FIG. 1;

FIG. 4 is a chart of experimental data showing dependence of a potentialof an upper electrode 55 and a potential of a lower electrode 53 shownin FIG. 1 on a self-alignment bias;

FIGS. 5A and 5B are schematic configuration diagrams of a plasmamonitoring system 50A according to Example 2 of the invention;

FIG. 6 is a schematic cross-sectional view of a plasma process detectionsensor according to Example 3 of the invention;

FIG. 7 is a schematic configuration diagram of a conventional plasmamonitoring system; and

FIG. 8 is a schematic diagram explaining the self-alignment bias.

DETAILED DESCRIPTION OF THE INVENTION Example 1 Plasma Monitoring SystemAccording to Example 1

FIG. 2 is a schematic configuration diagram of a plasma monitoringsystem according to Example 1 of the present invention.

The plasma monitoring system includes a plasma processing apparatus 30.The plasma processing apparatus 30 is an apparatus that generates plasma32 within a plasma chamber 31 set in a vacuum by applying an RF bias tothe plasma chamber 31. The plasma processing apparatus 30 performs suchprocessings as etching and film formation on a wafer 40 such as asemiconductor wafer, e.g., a silicon wafer disposed on a conductivestage 33 and serving as a monitoring target workpiece. A voltmeter 35for self-alignment bias measurement is connected to the stage 33 via acoil 34 for AC voltage component elimination. Two plasma processdetection sensors 50 (50-1, 50-2) are bonded onto a predeterminedportion or plural different portions (bonded onto two portions in FIG.2, respectively) on a surface of the wafer 40.

FIG. 1 is a schematic cross-sectional view of each of the plasma processdetection sensors 50 shown in FIG. 2 according to Example 1 of theinvention.

This plasma process detection sensor 50 has a substrate (e.g., siliconsubstrate) 51 and an insulating film 52 having a thickness of about 1.0μm, made of silicon oxide (SiO2 film), and formed on the siliconsubstrate 51. A first electrode (e.g., lower electrode) 53 having athickness of about 300 nm and made of a conductive matter such aspolysilicon (Poly-Si) is selectively formed on the insulating film 52.An insulating film 54 having a thickness of about 1.0 μm and made ofsilicon oxide is deposited on the first electrode 53. A second electrode(e.g., an upper electrode) 55 having a thickness of about 300 nm andmade of a conductive material such as polysilicon is selectively formedon the insulating film 54. A contact hole pattern for plural contactholes 56 to be actually formed in the wafer 44 and each having acircular cross section is formed on the upper electrode 55. A diameterof the circular cross section of each of the contact holes 56 is about100 nm. The contact hole 56 has a depth of about 1.3 μm measured from asurface of the upper electrode 55 to a surface of the lower electrode53.

A wiring connection area 57 is opened in an exposed portion of thesurface of the insulating film 54 and the surface of the lower electrode53 is exposed from the wiring connection area 57. A wiring 58 isconnected to the upper electrode 55 and a wiring 59 is connected to thelower electrode 53, and the two wirings 58 and 59 are led outside of theplasma chamber 31 shown in FIG. 2 via terminals (not shown),respectively. A voltmeter 60 for measuring potential is connected to thewiring 58 led outside. The voltmeter 60 is connected to a terminal 62having a reference potential (e.g., ground potential). Similarly, avoltmeter 61 measuring potential is connected to another wiring 59. Thevoltmeter 61 is connected to a terminal 63 having a reference potential(e.g., ground potential).

Method of Manufacturing the Sensor According to Example 1

FIGS. 3A to 3I are schematic cross-sectional views showing each one ofthe steps of a method of manufacturing each of the sensors 50 shown inFIG. 1. The sensor 50 shown in FIG. 1 is, for example, manufactured bythe following steps (FIGS. 3A to 3I).

In an insulating film formation step (FIG. 3A), the insulating film 52having the thickness of about 1.0 μm and made of silicon oxide is formedon the silicon substrate 51 by thermal oxidation. In a conductive filmformation step (FIG. 3B), a conductive film 53 a having a predeterminedimpurity ion concentration, having a thickness of about 300 nm, and madeof polysilicon is formed on the insulating film 52 by a chemical vapordeposition (hereinafter, “CVD”) method. In an electrode formation step(FIG. 3C), a mask for an electrode pattern which is made of a resistfilm is formed on the conductive film 53 a by photolithography. Theconductive film 53 a is then etched by dry etching such as plasmaetching to form the lower electrode 53, and the unnecessary mask isremoved by ashing.

In an insulating film formation step (FIG. 3D), the insulating film 54having the thickness of about 1.0 μm and made of silicon oxide isdeposited by the CVD method. In a conductive film formation step (FIG.3E), similarly to the conductive film formation step (FIG. 3B), aconductive film 55 a having a predetermined impurity ion concentration,having the thickness of about 300 nm, and made of polysilicon is formedon the insulating film 54 by the CVD method. In an electrode formationstep (FIG. 3F), similarly to the electrode formation step (FIG. 3C), amask for an electrode pattern made of a resist film is formed on theconductive film 55 a by the photolithography, and the conductive film 55a is etched by the dry etching such as plasma etching to form the upperelectrode 55.

In a contact hole formation step (FIG. 3G), a resist pattern is formedon the upper electrode 55 by the photolithography, and the upperelectrode 55 and the insulating film 54 are etched by a depth up to thesurface of the lower electrode 53 using the resist pattern as a mask bythe dry etching such as plasma etching, thereby forming the contact holepattern of plural contact holes 56 each having a circular cross section.The diameter of a circular cross section of each contact hole 56 isabout 100 nm and the depth of the contact hole 56 is about 1.3 μm. In awiring connection area opening step (FIG. 3H), the insulating film 54 isetched from the exposed surface to the surface of the lower electrode 53by the photolithography and by the dry etching to open the wiringconnection area 57.

Thereafter, in a wiring connection step (FIG. 3I), the wirings 58 and 59are connected to the upper electrode 55 and the lower electrode 53 andto the voltmeters 60 and 61 provided outside of the plasma chamber 31shown in FIG. 2, respectively.

Plasma Monitoring Method According to Example 1

Plural (e.g., two) sensors 50 each having the actual contact holepattern manufactured as stated above is prepared. The two sensors 50(50-1, 50-2) are bonded onto the two different portions on the surfaceof the wafer 40 shown in FIG. 2, respectively, and the resultantsensor-added wafer 40 is mounted on the stage 33 within the plasmachamber 31 in the plasma processing apparatus 30. An internal pressureof the plasma chamber 31 is set to, for example, 120 mTorr. A mixturegas of CHF3, CF4, N2, and Ar is filled into the plasma chamber 31 as afiller gas. The RF bias at 1600 W is applied to the plasma processingapparatus 30. Here, the plasma 32 is generated in the plasma chamber 31,and the wafer 40 is exposed to the plasma 32.

If the wafer 40 is exposed to the plasma 32, charge-up occurs at thebottoms of each of the contact holes 56 in the respective sensors 50(50-1 and 50-2) due to an electron blocking effect (electron shadingeffect) as shown in FIG. 1. Namely, more electrons e are trapped at theupper electrode 55 than at the lower electrode 53, thereby causing acharge bias between the surface of the contact hole pattern and thebottoms of each of the contact holes 56. Due to this, the upperelectrode 55 and the lower electrode 53 have different potentials. Atthis time, one or both of the upper electrode 55 and the lower electrode53 is measured by the voltmeters 60 and 61, respectively or a potentialdifference Δ(V2−V1, where V1 is a value indicated by the voltmeter 60and V2 is a value indicated by the voltmeter 61) between the upperelectrode 55 and the lower electrode 53 is measured by the voltmeters 60and 61, and monitored.

At this time, if a self-alignment bias Vdc is generated in theatmosphere of the plasma 32, the self-alignment bias Vdc is applied tothe portions (such as the outer circumference) of the conductive stage33 which portions are exposed to the plasma 32. Since the voltmeter 35is disposed below the stage 33 and connected to the stage 33, theself-alignment bias Vdc is read by the voltmeter 35. In this way, theself-alignment bias Vdc is measured with the entire area of theplasma-exposed portions of the stage 33 (such as the outer circumferenceof the stage 33) used as an antenna.

Advantages of Example 1

FIG. 4 is a chart of experimental data showing the dependence of thepotentials of the upper electrode 55 and the lower electrode 53 shown inFIG. 1 on the self-alignment bias. In FIG. 4, the horizontal axisindicates the self-alignment bias Vdc (V) and the vertical axisindicates the potentials (V) of the upper electrode 55 and the lowerelectrode 53.

According to Example 1, in each of the sensors 50 (50-1, 50-2), theupper electrode 55 and the lower electrode 53 are provided on thesurface of the actual contact hole pattern and the bottoms of thecontact holes 56, and the potentials of the surface of the contact holepattern and the bottoms of the contact holes 56 are measuredsimultaneously using the voltmeters 60 and 61. Due to this, as can beunderstood from the experimental data shown in FIG. 4, the charge-upoccurring in the actual contact pattern may be observed as the potentialdifference between the upper electrode 55 and the lower electrode 53.Besides, since the potential difference is measured during occurrence ofthe plasma 32, the charge-up may be observed at real time. Therefore,process conditions may be optimized and a reduction in yield caused bythe charge-up may be prevented.

Furthermore, as can be understood from the experimental data shown inFIG. 4, the potential of the upper electrode 55 has a correlation withthe self-alignment bias Vdc measured by the voltmeter 35 shown in FIG.2. Since the sensors 50-1 and 50-2 are arranged in plural differentportions (e.g., two portions) in the plane of the wafer 40,respectively, the in-plane distribution of the self-alignment bias Vdcmay be monitored indirectly. To improve monitoring accuracy, it sufficesto increase the number of sensors 50 installed in the plasma processingapparatus 30.

Example 2 Configuration of Plasma Monitoring System According to Example2

FIGS. 5A and 5B are schematic configuration diagrams of a plasmamonitoring system according to Example 2 of the invention. In FIGS. 5Aand 5B, the same constituent elements as those shown in FIGS. 1 and 2according to Example 1 are denoted by the same reference symbols,respectively.

The sensors 50 (=50-1 to 50-5) described in Example 1 are bonded ontoeach of plural (e.g., two) wafers 40-1 and 40-2. At this time, thesensor-added wafers 50-1 and 50-2 are configured so as to differ to eachother in the total area of contact holes 56 in the sensors 50 on thewafer 40-1 and 40-2, which is defined as (area of cross-sectional circleof one contact hole 56)×(number of contact holes 56 on the wafer 40-1and 40-2). For example, in FIGS. 5A and 5B, the number of sensors 50arranged on the wafers 40-1 and 40-2 are different. In FIG. 5A, the twosensors 50-1 and 50-2 are arranged in the plane of the wafer 40-1. InFIG. 5B, the five sensors 50-1 to 50-5 are arranged in the plane of thewafer 40-2. By such arrangement, the total area of the contact holes 56in the sensors 50-1 to 50-5 arranged on the wafer 40-2 is 2.5 times aslarge as that of the contact holes 56 in the sensors 50-1 and 50-2arranged on the wafer 40-1.

(Plasma Monitoring Method According to Example 2)

The two wafers 40-1 and 40-2, in which the sensors 50 are arranged, areexposed to the plasma 32 in the same conditions. Namely, the firstsensor-added wafer 40-1 is disposed within the plasma chamber 31,exposed to the plasma 32 in certain conditions, and taken out from theplasma chamber 31. The second sensor-added wafer 40-2 is then disposedwithin the plasma chamber 31 and exposed to the plasma 32 in the sameconditions as those for the first wafer 40-1.

As a result of the exposure of the wafer 40-2 to the plasma 32,charge-up occurs on the bottoms of the contact holes 56 of the sensors50 by the electron blocking effect (electron shading effect). Due tothis, the upper electrode 55 and the lower electrode 53 of each of thesensors 50 have different potentials. At this time, the potentialdifference between the upper electrode 55 and the lower electrode 53 ofeach of the sensors 50 arranged on the each of the wafers 40-1 and 40-2is measured by the voltmeters 60 and 61, and monitored.

Examples of a method of measuring the potential difference between theupper electrode 55 and the lower electrode 53 of a single sensor 50 areas follows. In a first method, the voltmeters 60 and 61 are connected toa single sensor 50 and measure the potentials, respectively. Thepotentials measured by the voltmeters 60 and 61 are compared with eachother (the potential difference is calculated). In a second method, onevoltmeter (having two terminals for measuring potentials of twoelectrodes) is connected to the two electrodes, i.e., the upperelectrode 55 and the lower electrode 53 of the single sensor 50, and thevoltage (potential difference) between the two electrodes is directlymeasured. As can be seen, it is necessary to use two voltmeters persensor to measure potentials using the voltmeters according to the firstmethod. It is necessary to use a single voltmeter per sensor to measurepotentials using the voltmeter according to the second method. Either ofthe first and second methods may be adopted.

Advantages of Example 2

According to Example 2, by comparing the potential differences measuredwith respect to the sensor-added wafers 40-1 and 40-2, where therespective contact holes 56 of the sensors 50 arranged respectively onthe wafers have different total areas, the dependence of the charge-upon the pattern ratio (dependence of the charge-up on the total area ofthe contact holes 56 per wafer) may be observed.

Namely, if a plasma etching target area is larger, the amount of plasmagas consumed for the plasma etching is normally larger (because of alarge amount of reaction gas reacting with the etching targetworkpiece). In this case, if the supply amount of the plasma gasrelative to the consumption amount is insufficient, plasma etch ratedecelerates. The deceleration of the etch rate due to an increase in theconsumption amount relative to the supply amount of the plasma gas isreferred to as “loading effect”. The loading effect is confirmed bymeasuring the dependence of the etch rate on the pattern ratio(dependence of the etch rate on the etching target area).

Similarly to Example 1, according to Example 2, it is considered thatthe insulating film and the like on inner sidewalls of the contact holes56 in the sensors 50 are slightly etched. Due to this, if the area ofthe contact holes 56 present in the wafers 40-1 and 40-2 is larger(e.g., the number of contact holes 56 is larger or the diameter of eachcontact hole 56 is larger), the amount of gas reacting with theinsulating film and the like on the sidewalls of the contact holes 56 islarger (i.e., the amount of gas consumed in the contact holes 56 out ofthe plasma 32 within the plasma chamber 31 increases). As a result, thestate of the plasma 32 (“plasma state”) within the plasma chamber 31changes. It is considered, therefore, that charge-up change derivingfrom the change in the plasma 32 occurs. By observing the dependence ofthe charge-up on the pattern ratio, therefore, the plasma state may beappropriately monitored.

Example 3

FIG. 6 is a schematic cross-sectional view of a plasma process detectionsensor 50A according to Example 3 of the invention. In FIG. 6, the sameconstituent elements as those shown in FIG. 1 according to Example 1 aredenoted by the same reference symbols, respectively.

One or more intermediate electrodes may be provided between the upperelectrode 55 and the lower electrode 53 in each of the sensors 50according to Example 1 and Example 2. FIG. 6 shows an instance ofadditionally providing one intermediate electrode according to Example3.

In the sensor 50A according to Example 3, an intermediate electrode 64having a predetermined impurity ion concentration, having a thickness ofabout 300 nm, and made of polysilicon is formed in the insulating film54 between the lower electrode 53 and the upper electrode 55. Avoltmeter 66 is connected to the intermediate electrode 64 by a wiring65, and connected to a terminal 67 having a reference potential (e.g.,ground potential).

Charge-up occurs onto the inner walls of the contact holes 56 by theplasma 32. Due to this, if the contact holes 56 are formed in an LSIproduct or the like by plasma etching, a phenomenon occurs that positiveions h accelerating etching are influenced by the potential of the innerwalls of the contact holes 56 so that a path of the positive ions h iscurved in a direction of the bottoms of the contact holes 56 and thepositive ions h strike against the inner walls of the contact holes 56,and that the inner walls are etched. If the inner walls of the contactholes 56 are conspicuously etched, problems such as a reduction inproduct yield occur. Since the potential of the inner walls of thecontact holes 56 has an influence on the path of the positive ions hfrom the plasma 32, the potential of the inner walls of the contactholes 56 between the upper electrode 55 and the lower electrode 53 maybe measured by providing the intermediate electrode 64 and the charge-upin the contact holes 56 may be examined in more detail.

If two or more intermediate electrodes 64 are provided, the intermediateelectrodes 64 may be provided at positions set by dividing equally,e.g., trisecting or quadrisecting the interval between the upperelectrode 55 and the lower electrode 53, respectively or at positionsbetween the upper electrode 55 and the lower electrode 53 at whichpositions the potential is to be measured, respectively.

Modifications

The invention is not limited to Example 1 to Example 3. Variousmodifications may be made of the invention and the invention may becarried out in various types of use. Examples of the types of use andmodifications include (i) to (iv) as follows.

(i) In the invention, the configurations, manufacturing methods and thelike of the plasma processing apparatus 30 and the sensors 50 and 50Ashown in the drawings may be changed.

(ii) In FIG. 2, the two sensors 50-1 and 50-2 are provided on thesurface of the wafer 40. Alternatively, one sensor 50-1 may be providedon the surface of the wafer 40 or near the wafer 40 (e.g., on the outercircumference of the stage 33) depending on usage. Likewise, in FIGS. 5Aand 5B, plural sensors 50 is provided respectively on the surface ofeach of the wafers 40-1 and 40-2. Alternatively, one sensor 50-1 may beprovided on the wafer 40-1 or 40-2 while changing the number of contactholes 56 formed in the sensors 50 and the plasma process may bemonitored.

(iii) The plasma monitoring system shown in FIG. 2 includes the plasmaprocessing apparatus 30. Alternatively, the plasma monitoring system maybe configured to include the sensor 50 and the voltmeters 60 and 61shown in FIG. 1 or to include the sensor-added wafer 40 to which one ormore sensors 50 is attached and the voltmeters 60 and 61. At this time,if the voltmeters 60 and 61 are downsized and the downsized voltmeters60 and 61 and the other circuit components (such as a driving batteryand a data storage memory) are included in the sensor 50 or thesensor-added wafer 40, the plasma monitoring system may be downsized anduser-friendliness of the plasma monitoring system is improved.

(iv) In Example 1 to Example 3, the semiconductor manufacturing processusing plasma has been described. However, the invention is applicable toall the other manufacturing processes using plasma than thesemiconductor manufacturing process, for example, to a flat panelmanufacturing process.

As can be understood from the foregoing, according to the invention, thesecond electrode (upper electrode 55) and the first electrode (lowerelectrode 53) are provided on the surface of the actual contact holepattern and the bottoms of the contact holes (56), respectively, and thepotential of the surface of the contact hole pattern and the potentialof the bottoms of the contact holes are measured simultaneously.Therefore, the charge-up occurring in the actual contact hole patternmay be observed as the potential difference between the second electrodeand the first electrode. Besides, since the potential difference ismeasured during occurrence of the plasma (32), the charge-up may beobserved at real time. Therefore the process conditions may be optimizedand the reduction in yield caused by the charge-up may be suppressed.

Moreover, the potential of the second electrode has a correlation withthe self-alignment bias measured on the plasma processing apparatus. Dueto this, if sensors are arranged, for example, in a plurality portionsin the plane of the wafer, respectively, the in-plane distribution ofthe self-alignment bias may be monitored indirectly.

What is claimed is:
 1. A plasma monitoring method comprising: a firstplasma processing including: preparing a first wafer to be monitored;arranging and bonding a plurality of sensors on the first wafer, each ofthe plurality of sensors comprising: a substrate; a first electrodeformed on the substrate; an insulating film that is formed on the firstelectrode and has a contact hole formed therein, the contact holeexposing a part of a surface of the first electrode; and a secondelectrode that is formed on the insulating film and is electricallyseparated from the first electrode; positioning the first wafer in aspace where plasma is generated during the first plasma processing; andmonitoring the plasma by measuring potentials of the first electrode andthe second electrode of each of the sensors, or a potential differencebetween the first electrode and the second electrode of each of thesensors during the first plasma processing to determine charge-up; asecond plasma processing that is performed before the first plasmaprocessing or after the first plasma processing, the second plasmaprocessing including: preparing a second wafer to be monitored;arranging and bonding a group of the sensors on the second wafer at aplurality of different positions on the second wafer, a total number ofthe group of the sensors arranged and bonded on the second wafer isdifferent from a total number of the plurality of sensors arranged andbonded on the first wafer; and positioning the second wafer in a spacewhere plasma is generated during the second plasma processing; andmonitoring the plasma generated during the second plasma processing bymeasuring potentials of the first electrode and the second electrode ofeach of the group of the sensors that are arranged and bonded on thesecond wafer, or a potential difference between the first electrode andthe second electrode of each of the group of the sensors that arearranged and bonded on the second wafer to determine charge-up; anddetermining a dependence of charge-up on a pattern-ratio by comparingcharge-up changes during the first plasma processing and the secondplasma processing.
 2. The plasma monitoring method of claim 1, wherein atotal area of the contact holes of the plurality of sensors arranged andbonded to the first wafer is different than a total area of the contactholes of the group of the sensors arranged and bonded to the secondwafer.
 3. The plasma monitoring method of claim 1, further comprisingaccommodating the first and second wafers within a plasma chamber. 4.The plasma monitoring method of claim 1, wherein each of the sensors ofthe plurality of sensors arranged and bonded to the first wafer has oneor more third electrodes arranged between the first electrode and thesecond electrode and electrically isolated from the first electrode andthe second electrode, and the method further comprises: during the firstplasma processing, for each of the respective sensors of the pluralityof sensors arranged and bonded to the first wafer, measuring andmonitoring at least one of potentials of the first, second and thirdelectrodes of the respective sensor, or a potential difference among thefirst, second and third electrodes of the respective sensor; and duringthe second plasma processing, for each of the respective sensors of thegroup of the sensors arranged and bonded to the second wafer, measuringand monitoring at least one of potentials of the first, second and thirdelectrodes of the respective sensor, or a potential difference among thefirst, second and third electrodes of the respective sensor.
 5. Theplasma monitoring method of claim 1, wherein each of the contact holeshas a cross-section of a circle.
 6. The plasma monitoring method ofclaim 1, wherein each of the plurality of sensors arranged and bonded tothe first wafer further comprises a plurality of contact holes.
 7. Theplasma monitoring method of claim 1, wherein the first plasma processingincludes modifying process conditions of the first plasma processing soas to suppress over-etching the contact holes of the plurality ofsensors arranged and bonded to the first wafer during the first plasmaprocessing.
 8. The plasma monitoring method of claim 7, wherein thesecond plasma processing includes modifying process conditions of thesecond plasma processing so as to suppress over-etching the contactholes of the group of the sensors arranged and bonded to the secondwafer during the second plasma processing.
 9. The plasma monitoringmethod of claim 1, wherein in the first plasma processing, themonitoring the plasma includes measuring the potential differencebetween the first electrode and the second electrode of each of theplurality of sensors arranged and bonded to the first wafer during thefirst plasma processing to determine charge-up, and the monitoring theplasma generated during the second plasma processing includes measuringthe potential difference between the first electrode and the secondelectrode of each of the group of the sensors that are arranged andbonded on the second wafer to determine charge-up.
 10. The plasmamonitoring method of claim 1, wherein the first plasma processing andthe second plasma processing are performed in a same chamber.